Heat stroke is also known as sunstroke, thermic fever, or siriasis. It happens when the body's mechanisms for controlling temperature fail. Heat stroke is a life-threatening emergency needing immediate treatment. While many people feel sick and faint during heat waves, most of these people are suffering from heat exhaustion, a related condition usually less serious than heat stroke.
There are two types of heat stroke: classic, non-exertional heat stroke (NEHS) and exertional heat stroke (EHS). Classic heat stroke occurs most commonly in very young or older individuals, who have health risks and are in poor environmental conditions. Exertional heat stroke occurs more often in younger, healthy individuals who participate in strenuous physical activity.
Working or exercising in hot conditions or weather without drinking enough fluids is the main cause of heat stroke. You can get heat stroke by not replacing lost fluids over days or weeks, or you can bring it on in a few hours by exercising strenuously on a hot day without drinking plenty of liquids first.
Liquids help to cool us down by allowing the body to produce sweat. However, liquids are also necessary for bodily functions, such as keeping up blood pressure. You can lose large amounts of body fluid in the form of sweat without noticing any effects, but at a certain point the body will reserve the remaining fluid for vital functions and stop sweating. The body's core temperature then shoots up, and cells start dying.
Sweat evaporates more rapidly in dry weather, cooling the body more efficiently than in humid weather. When working in humid conditions, the core temperature rises more rapidly. This is why weather forecasts add a humidity factor or heat index to represent how you will actually feel outdoors.
People with the following conditions are especially prone to heat stroke:
Heavy clothing and some skin conditions can also contribute to the occurrence of heat stroke.
The symptoms of heat stroke are quite different from those of heat exhaustion.
Symptoms of heat exhaustion:
A person suffering from heat exhaustion will usually be sweating profusely in an attempt to get rid of excess heat.
Symptoms of heat stroke:
Someone with heat stroke has stopped sweating, due to a failure in his or her heat control system.
High core temperatures damage the internal organs, especially the brain. The fluid loss can also produce dangerously low blood pressure. Most people who are killed by heat stroke die when their heart stops pumping effectively (circulatory failure). Even people who survive are likely to have permanent brain damage if their core temperature has been over 40.6°C (105°F) for more than an hour or two.